4 Troubleshooting
4.1 Troubleshooting Tips
Before attempting to repair a frequency converter, here are
some tips to follow to make the job easier and possibly
prevent unnecessary damage to functional components.
1.
Ensure that no voltage is present on the
frequency converter prior to troubleshooting.
Check for the presence of AC input voltage and
DC bus voltage and ensure there is none before
working on the unit. Remember that voltage may
be present for as long as 40 minutes after
removing power from the unit. See the label on
the front of the frequency converter door for the
specific discharge time. Some points in the
frequency converter are referenced to the
negative DC bus and are at bus potential even
though it may appear on diagrams to be a
neutral reference.
2.
If any of the DC bus fuses are blown, always
ensure no DC bus voltage is present on either
side of the DC fuses. When any DC bus fuse is
blown, capacitor banks in the other inverter
modules are no longer electrically connected. As
a result, one inverter module may have stored
voltage even when the rest of the unit has none.
3.
Darkened LED lights on the LCP does not mean
that the drive has no dangerous internal voltage.
Do not assume the unit contains no voltage
when the indicator lights are off.
4.
Never apply power to a unit that is suspected of
being faulty. Many faulty components within the
frequency converter can cause damage to other
components when power is applied. Always
perform the procedure for testing the unit after
repair as described in Section
Test Procedures
.
5.
With an external power supply and cable
assembly, the logic section of the frequency
converter can be powered without applying
power to the rest of the unit. This method of
power isolation is recommended for trouble-
shooting logic problems.
6.
Never attempt to defeat any fault protection
circuitry within the frequency converter. That will
result in unnecessary component damage and
may cause personal injury.
7.
Always use factory approved replacement parts.
The frequency converter has been designed to
operate within certain specifications. Incorrect
parts may affect tolerances and result in further
damage to the unit.
8.
Read the instruction and service manuals. A
thorough understanding of the unit is the best
approach. If ever in doubt, consult the factory or
authorized repair centre for assistance.
4.2 Exterior Fault Troubleshooting
There may be slight differences in servicing a frequency
converter that has been operational for some extended
period of time compared to a new installation. When using
proper troubleshooting procedures, make no assumptions.
To assume a motor is wired properly because the
frequency converter has been in service for some time may
cause you to overlook issues like loose connections,
improper programming, or added equipment,. It is best to
develop a detailed approach, beginning with a physical
inspection of the system. See Table
Visual Inspection
for
items to examine.
4.3 Fault Symptom Troubleshooting
This troubleshooting section is divided into sections based
on the symptom being experienced. To start the following
table provides a visual inspection check list. Many times
the root cause of the problem may be due to the way the
frequency converter has been installed or wired. The check
list provides guidance through a variety of items to inspect
during any frequency converter service process.
Next, symptoms are approached as the technician most
commonly discovers them: reading an unrecognised
frequency converter display, problems with motor
operation, or a warning or alarm displayed by the
frequency converter. Remember, the frequency converter
processor monitors inputs and outputs as well as internal
frequency converter functions, so an alarm or warning
does not necessary indicate a problem within the
frequency converter itself.
Each incident has further descriptions on how to
troubleshoot that particular symptom. When necessary,
further referrals are made to other parts of the manual for
additional procedures. The section
Frequency Converter and
Motor Applications
presents detailed discussions on areas
of frequency converter and system troubleshooting that an
experienced repair technician should understand in order
to make effective diagnoses.
Finally, a list of tests called After Repair Tests is provided.
These tests should always be performed when first starting
Troubleshooting
High Power Service Manual for Modular F Frame Drives
MG90K202 - VLT
®
is a registered Danfoss trademark
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